Wave your hand to lock and unlock the screen, a few minor glitches but great concept.

Air Lock Screen
Developer: ZUI
Category: tools
Google play Rating: 3.9
Install from Google Play

Air Lock Screen

Would you like to free your power button, lock and unlock your device without touch it?
Just try Air Lock Screen! Swipe your hand on top of your phone and see the magic!

– Lock/Unlock screen with hand swipe.
– Three lock mode supported (desktop only, all apps mode and white list mode).
– Enable/Disable app in notification center. 
– Disable in landscape to prevent screen lock when playing game or watching video.